Track-module apparatus with load-independent load distribution

ABSTRACT

In vehicle track-module apparatus including a module frame, a drive wheel rotatable with respect to the frame, ground-engaging leading and trailing wheels, at least one ground-engaging bogie wheel, and an endless track extending around the wheels and driven by its engagement with the drive wheel, the improvement comprising: (a) a leading suspension arm rotatable with respect to the frame and extending forwardly to a distal end at which a leading-wheel assembly is rotatably attached and rearwardly to a rearward suspension end; (b) a trailing suspension arm rotatable with respect to the frame and extending rearwardly to a distal end at which a trailing-wheel assembly is rotatably attached and forwardly to a forward suspension end; (c) a bogie assembly having a bogie mount and the at least one bogie wheel rotatable with respect thereto; and (d) leading and trailing suspension elements rotatably attached to and extending from the rearward and forward suspension ends, respectively, to rearward and forward rotatable bogie-mount connections, respectively.

FIELD OF THE INVENTION

The invention relates generally to the field of vehicle track-modulesystems of the type typically for use in place of vehicle wheels and,more particularly, to track modules having leading and trailing wheelsand at least one load-supporting bogie wheel between the leading andtrailing wheels, all of which are engaged by an endless track extendingaround the wheels to drive a vehicle along the ground.

BACKGROUND OF THE INVENTION

Agricultural vehicles such as tractors, combines and the like arecommonly used in agricultural fields for a variety of jobs, andconstruction vehicles and other large work vehicles are used for manydifferent jobs on a variety of ground surfaces. Typically, thesevehicles have large wheels with tires on which the vehicles aresupported on the ground. However, for improved traction, vehicletrack-module systems (or “track modules” or “track-module apparatus”)are used in place of wheels with tires, and such track-module systemsprovide a much larger ground-surface engagement area supporting vehicleweight and tends to prevent vehicles from becoming bogged down in mud orother soft ground surfaces.

Among the challenges encountered in the use of vehicle track-moduleapparatus is the need to distribute the load supported by the trackmodule among the various wheels. These loads are both static and dynamicand may change during operation of the vehicle. Loads change as thevehicle encounters uneven ground, as the vehicle turns and as the slopeof the ground being traversed changes. Ideally, all wheels remain incontact with the ground through the endless belt and share a portion ofthe load at all times.

One track-module unit which is intended to distribute load relativelyevenly is disclosed in U.S. Pat. No. 7,628,235 (Satzler et al.) owned byCLAAS Industrietechnik GmbH of Paderhorn, Germany. A vehicle trackroller unit is disclosed which has at least one pivotable subframe andat least one further pivotable subframe, and each of the subframesrotatably accommodates at least one land wheel. At least one subframe ispivotably mounted on the vehicle, and the at least one further subframeis pivotably mounted on the at least one pivotable subframe.

Another vehicle track-module unit is disclosed in United StatesPublished Patent Application No. 2013/0154345 (Schultz et al.) owned byCLAAS Selbstfahrende Erntemaschinen GmbH of Harsewinkel, Germany. Avehicle track unit is disclosed which has a plurality of supportingrollers arranged one behind the other in the direction of travel of thevehicle and around which a belt is wrapped. The rollers are adjusted byway of at least one actuator between a first configuration, in which allsupporting rollers are loaded, and a second configuration, in which atleast one outer roller of the supporting rollers is relieved. An energysource delivers drive energy required to adjust the configuration. Anenergy accumulator is charged by the drive energy source and connectedto the actuator in order to provide the actuator with the drive energyrequired to adjust the configuration.

CLAAS also has its Lexion Terra Trac product line which includesconfigurations which are intended to address some of these challenges.However, none of these prior art systems includes all of the elements ofthe present invention and meets the needs as outlined above.

OBJECTS OF THE INVENTION

It is an object of this invention to provide an improved vehicletrack-module apparatus which has high load-supporting capability whilemaintaining lower contact forces on the ground by providing lowerloading per axle from more even load distribution.

Another object of this inventive vehicle track-module apparatus is tominimize the unsprung mass of the track-module apparatus.

Another object of the inventive vehicle track-module apparatus is toprovide track-module apparatus which shares load changes between axles.

A further object of the inventive vehicle track-module apparatus is toprovide track-module apparatus in which each axle is able to movevertically in an independent manner.

Yet another object of the inventive vehicle track-module apparatus is toprovide track-module apparatus in which the load distribution on thewheels is independent of vertical load.

Still another object of the inventive vehicle track-module apparatus isto provide track-module apparatus which has independent roll-modemovement for all bogie axes.

An additional object of this invention is to provide improved vehicletrack-module apparatus which includes an articulating bogie assembly andwhich includes independent accommodation of bogie roll motion.

Yet another object of the present invention is to provide track-moduleapparatus which reduces wear on the flexible track.

These and other objects of the invention will be apparent from thefollowing descriptions and from the drawings.

BRIEF SUMMARY OF THE INVENTION

This invention is an improvement in vehicle track-module apparatus whichincludes a module frame, a drive wheel rotatable with respect to theframe, leading and trailing ground-engaging wheels, at least oneground-engaging bogie wheel, and an endless track extending around thewheels and driven by its engagement with the drive wheel.

The inventive improvement comprises: (1) a leading suspension armrotatably attached to the frame at a leading arm axis and extendingforwardly to a leading-arm distal end at which a leading-wheel assemblyis rotatably attached and rearwardly to a rearward suspension end; (2) atrailing suspension arm rotatably attached to the frame at a trailingarm axis and extending rearwardly to a trailing-arm distal end at whicha trailing-wheel assembly is rotatably attached and forwardly to aforward suspension end; (3) a bogie assembly having a bogie mount andthe at least one leading bogie wheel rotatable with respect thereto; and(4) leading and trailing suspension elements rotatably attached to andextending from the rearward and forward suspension ends, respectively,to rearward and forward rotatable bogie-mount connections, respectively.

The term “axis” as used herein pertains to a pivot joint which includesthe necessary components such as bearings and other structure to permitrotation about such axis. A more complete description of the use of thisand related terms is presented later in this document.

The term “suspension elements” as used herein refers to components inthe suspension system which provide spring force and/or damping in thesystem.

The term “ground-engaging” as used herein with respect to a wheel meansthat the wheel bears on the ground through the endless track thatengages the wheel under normal operating conditions.

The term “bogie wheel(s)” as used herein refers to one or more wheelsproviding support for a vehicle in a middle ground-engaging region of atrack module, with other ground-engaging support being provided rearwardand/or forward of the bogie wheels(s).

The term “therebetween” when referring to the position ofground-engaging bogie wheels means that the bogie wheels are positionedbehind the leading ground-engaging wheel(s) and ahead of the trailingground-engaging wheel(s) along the direction of travel. The term “idler”as used herein refers to wheel which is not a driven wheel but turn onlyby virtue of its engagement with the endless track.

The term “load- and ground-responsive” as used herein with respect tosuspension joints means that the above-ground positions of such jointsare variable, including with respect to the frame, and depend on thecontour of the ground under the track and on the total loading on thetrack module, however caused.

In some preferred embodiments of the improved vehicle track-moduleapparatus, the leading-arm and trailing-arm axes coincide at asuspension-arm axis. In some such embodiments, the suspension-arm axisis at a level lower than the drive wheel axis, and in some of theseembodiments, the suspension-arm axis is rearward of drive wheel axis.

In highly-preferred embodiments, (a) the bogie assembly further includesa bogie-assembly arm rotatably attached (i) at a bogie-assembly armdistal end to the leading suspension arm at a first bogie-assembly axisbetween the leading-arm distal end and the suspension-arm axis and (ii)at a bogie-assembly arm proximal end to the bogie mount at a secondbogie-assembly axis, (b) the leading suspension element is rotatablyattached (i) to the rearward suspension end at a leadingsuspension-element pivot and (ii) to the rearward bogie-mount connectionat a first bogie-assembly pivot, and (c) the trailing suspension elementis rotatably attached (i) to the forward suspension end at a trailingsuspension-element pivot and (ii) to the forward bogie-mount connectionat a second bogie-assembly pivot.

In some of these highly-preferred embodiments, the at least one bogiewheel includes at least one leading bogie wheel and at least onetrailing bogie wheel, and the bogie mount includes (a) a bogie-mountforward portion having the at least one leading bogie wheel attachedthereto at a leading bogie axis, the bogie-mount forward portionincluding the forward bogie-mount connection, and (b) a bogie-mountrearward portion having the at least one trailing bogie wheel attachedthereto at a trailing-bogie axis, the bogie-mount rearward portionincluding the rearward bogie-mount connection. Some of these embodimentsmay also include at least two leading bogie wheels and at least twotrailing bogie wheels, and in these embodiments, the leading bogie axisrotates on a leading bogie roll axis perpendicular thereto and thetrailing bogie axis rotates on a trailing bogie roll axis perpendicularthereto.

In some of the preferred embodiments, the bogie-mount forward andrearward portions are rotatably attached at a third bogie-assembly axis,and in some of these embodiments, the bogie mount further includes abogie-mount middle portion having at least one middle bogie wheelattached thereto at a middle bogie axis.

In other highly-preferred embodiments, the inventive vehicletrack-module apparatus includes at least two leading bogie wheels, atleast two trailing bogie wheels, and at least two middle bogie wheelsand (a) the leading bogie axis rotates on a leading bogie roll axisperpendicular thereto, (b) the middle bogie axis rotates on a middlebogie roll axis perpendicular thereto, and (c) the trailing bogie axisrotates on a trailing bogie roll axis perpendicular thereto. In some ofthese embodiments, the bogie-mount forward and middle portions arerotatably attached at a third bogie-assembly axis.

In certain highly-preferred embodiments, the vehicle track-moduleapparatus further includes a tensioning element having first and secondends, the first end rotatably attached to the leading suspension arm ata proximal tensioning pivot between the leading-arm distal end and thesuspension-arm axis. In such embodiment, the leading-wheel assemblyincludes (a) at least one leading wheel rotatable about a leading-wheelaxis and (b) a wheel linkage at the leading-wheel axis. The distal endof the leading suspension arm is rotatably attached to the wheel linkageat a wheel offset axis offset from the leading-wheel axis and the secondend of the tensioning element is rotatably attached to the wheel linkageat a distal tensioning pivot offset from the leading-wheel axis. Also,the tensioning axes is angularly displaced therearound such that thewheel linkage is a class 2 lever with the wheel offset axis being thefulcrum thereof. In some of these embodiments, the trailing-wheelassembly includes a trailing-wheel axis at the trailing-arm distal endand at least one trailing wheel rotatable about the trailing-wheel axis.

In some highly-preferred embodiments, the rotatable attachments of theleading and trailing suspension elements at the rearward and forwardsuspension ends, respectively, are configured to permit rotation havingat least two degrees-of-freedom and the rearward and forward rotatablebogie-mount connections are configured to permit rotation having atleast two degrees-of-freedom.

In certain highly-preferred embodiments, the rotatable attachments ofthe first and second ends of the tensioning element are configured topermit rotation having at least two degrees-of-freedom.

In certain highly-preferred embodiments, the leading and trailingsuspension elements include gas-filled components to provide springforce. In some of these embodiments, the leading and trailing suspensionelements further include hydraulic piston and cylinder components. Also,in some of these embodiments, the leading and trailing suspensionelements are on a common hydraulic circuit. And some of theseembodiments further include an external accumulator hydraulicallyconnected to the common hydraulic circuit.

In certain embodiments of the inventive vehicle track-module apparatus,the leading and trailing wheels have equal diameters, and in someembodiments, the bogie wheels have equal diameters.

In another aspect of the invention, the leading wheel(s) are leadingidler wheel(s), the trailing wheel(s) are trailing idler wheel(s), thedrive wheel is positioned above and between the idler wheels, theleading-wheel assembly is a leading-idler assembly, and thetrailing-wheel assembly is a trailing-idler assembly.

Some embodiments of the inventive track-module apparatus are configuredsuch that the drive wheel is driven by a driving mechanism configured tobe powered by the vehicle, and in some of these embodiments, the drivingmechanism is a gearbox attachable to a driven axle of a vehicle.

Some embodiments of the inventive vehicle track-module apparatus includea tensioning element having first and second ends with the first endrotatably attached to the trailing suspension arm at a proximaltensioning pivot between the trailing-arm distal end and the trailingarm axis. In these embodiments, the trailing-wheel assembly includes (a)at least one trailing wheel rotatable about a trailing-wheel axis and(b) and a wheel linkage at the trailing-wheel axis. The distal end ofthe trailing suspension arm is rotatably attached to the wheel linkageat a wheel offset axis offset from the trailing-wheel axis; the secondend of the tensioning element is rotatably attached to the wheel linkageat a distal tensioning pivot which is offset from the trailing-wheelaxis; and the distal tensioning pivot and the wheel offset axis areangularly displaced around the trailing-wheel axis such that wheellinkage is a class 2 lever with the wheel offset axis being the fulcrumthereof. In some of these embodiments, the leading-wheel assemblyincludes a leading-wheel axis at the leading-arm distal end and at leastone leading wheel rotatable about the leading-wheel axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective drawing of an embodiment of the vehicletrack-module apparatus of this invention.

FIG. 1B is a perspective drawing of the embodiment of FIG. 1A as viewedfrom the side opposite that shown in FIG. 1A.

FIG. 2 is a perspective drawing of portions of the embodiment of thevehicle track-module apparatus of FIGS. 1A and 1B, illustrating thesuspension linkage components without the drive wheel, endless polymerictrack, wheels, frame and suspension elements.

FIG. 3 is an exploded perspective drawing of the embodiment of FIGS. 1Aand 1B.

FIG. 4 is a side-elevation drawing of the embodiment of FIGS. 1A and 1Bwith the near set of idler and bogie wheels removed to show thelinkages.

FIG. 5 is side-elevation drawing of portions of the embodiment of thevehicle track-module apparatus of FIGS. 1A and 1B, showing thesuspension linkage components without the drive wheel and the endlesstrack and wheels.

FIG. 6A is a perspective drawing of the bogie mount portions of thebogie assembly of the vehicle track-module apparatus of FIGS. 1A and 1B.

FIG. 6B is a perspective drawing of the bogie mount of FIG. 6A showingthe bogie-mount forward portion rotated with respect to the bogie-mountrearward portion around the third bogie-assembly axis.

FIGS. 7A-7F are side-elevation drawings of the embodiment of FIGS. 1Aand 1B illustrating the movement of the inventive vehicle track-moduleapparatus as it traverses over a small bump along its path of travel.FIG. 7A shows the track-module apparatus just prior to encountering thebump.

FIG. 7B shows the track-module apparatus with its leading idler wheelsover the bump.

FIG. 7C shows the track-module apparatus with its leading bogie wheelsover the bump.

FIG. 7D shows the track-module apparatus with its middle bogie wheelsover the bump.

FIG. 7E shows the track-module apparatus with its trailing bogie wheelsover the bump.

FIG. 7F shows the track-module apparatus with its trailing idler wheelsover the bump.

FIG. 8A is a side-elevation drawing of the embodiment of FIGS. 1A and 1Billustrating the movement of the inventive vehicle track-moduleapparatus as it traverses an uphill path.

FIG. 8B is a side-elevation drawing of the embodiment of FIGS. 1A and 1Billustrating the movement of the inventive vehicle track-moduleapparatus as it traverses a downhill path.

FIG. 9 is a schematic drawing of the leading and trailing suspensionelements in a hydraulic circuit.

FIG. 10 is a schematic diagram of the embodiment of FIGS. 1A and 1Billustrating the supported load FL and the five resulting wheel loads F1through F5.

FIG. 11 is a side-elevation drawing (similar to FIG. 4) of a firstalternative embodiment of the vehicle track-module apparatus of thisinvention. Such embodiment is similar to the embodiment of FIG. 4 butincludes only leading and trailing bogie wheels with correspondingmodifications to the components used in the suspension system.

FIG. 12 is a side-elevation drawing (similar to FIG. 4) of a secondalternative embodiment of the vehicle track-module apparatus of thisinvention. Such embodiment is similar to the embodiment of FIG. 11 butdoes not include a tensioning element and the leading-idler assemblyincludes only the leading idler wheel.

FIG. 13 is a side-elevation drawing (similar to FIG. 4) of a thirdalternative embodiment of the vehicle track-module apparatus of thisinvention. Such embodiment is similar to the embodiment of FIG. 4 butdoes not include a tensioning element and the leading-idler assemblyincludes only the leading idler wheel.

FIG. 14 is a side-elevation drawing (similar to FIG. 4) of a fourthalternative embodiment of the vehicle track-module apparatus of thisinvention. Such embodiment is similar to the embodiment of FIG. 13 butdoes not include the third bogie-assembly axis.

FIG. 15A is side-elevation drawing of portions of the embodiment of thevehicle track-module apparatus of FIG. 1 to illustrate the detail of anend of the tensioning element.

FIG. 15B is a sectional view of FIG. 15A.

FIG. 15C is an enlargement of a portion of FIG. 15B particularly showingan end of the tensioning element.

FIG. 16 is a table of reference numbers for the components and otherthings illustrated in FIGS. 1A-15C and 17A-18 and for the forcesrepresented in the drawings.

FIG. 17A is a table of dimensions for an exemplary track-moduleapparatus.

FIG. 17B is a set of five tables illustrating five different sets ofloads on the exemplary apparatus of FIG. 17A and the five resulting loaddistributions.

FIG. 18 is a schematic diagram of an embodiment of the inventivetrack-module apparatus in which a tensioning element is mounted withrespect to the trailing idler wheel.

DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS

FIG. 1A is a perspective drawing of an embodiment 10 of the vehicletrack-module apparatus of this invention. (As referred to herein, anembodiment of a track-module apparatus and the track-module apparatusitself may be referred to using the same reference number. Thus, forexample, “embodiment 10” and “track-module apparatus 10” refer to thesame apparatus.) Embodiment 10 includes a module frame 12, a drive wheel14 which is rotatable with respect to frame 12, the drive wheel having adrive wheel axis 16, ground-engaging leading wheels 18 andground-engaging trailing wheels 20 and ground-engaging bogie wheels 56,60 and 64, and an endless track 22 which extends around wheels 14, 18,20, 56, 60 and 64 and is driven by its engagement with drive wheel 14.

FIG. 1B is a perspective drawing of track-module apparatus 10 of FIG. 1Aas viewed from the side opposite that shown in FIG. 1A. Referring toFIG. 1B, track-module apparatus 10 includes a vehicle connection 11 atwhich track-module apparatus 10 is attached to a vehicle and a drivegearbox 14 g which receives power from the vehicle through a drive powerinput shaft 14 p.

In embodiment 10, leading wheels 18 are leading idler wheels 18, andtrailing wheels 20 are trailing idler wheels 20. In some embodiments ofthe inventive track-module apparatus, it is contemplated that a leadingor trailing wheel may also function as the drive wheel. Also inembodiment 10, endless track 22 is an endless polymeric track 22. It iscontemplated that within the scope of the present invention, endlesstrack 22 may be constructed of a wide variety of materials andstructures including metallic components such as are presently known insome tracked vehicles. The specific properties and materials of theendless track are not central to the inventive concepts of the presentinvention.

Bogie wheels 56 are leading bogie wheels, bogie wheels 60 are trailingbogie wheels, and bogie wheels 64 are middle bogie wheels. Bogie wheels56, 60 and 64 are part of a bogie assembly 46. Embodiment 10 alsoincludes a leading suspension arm 24, a trailing suspension arm 34, aleading suspension element 68, a trailing suspension element 70, and atensioning element 106.

The direction of forward travel of the track module of embodiment 10(and other similar embodiments presented herein) is defined by leadingidler wheels 18 being ahead of trailing idler wheels 20. FIG. 4 includesan arrow 122 indicating the direction of travel applicable to allembodiments as defined by the leading and trailing components of theembodiments.

FIGS. 2 through 6B illustrate track-module apparatus 10 and variouspartial assemblies thereof in several views in order to show moreclearly the various aspects of inventive track-module apparatus 10. FIG.2 is a perspective drawing of portions of track-module apparatus 10,illustrating the several suspension linkage components without drivewheel 14, track 22, leading idler wheels 18, trailing idler wheels 20,leading bogie wheels 56, trailing bogie wheels 60, middle bogie wheels64, frame 12, leading suspension element 68, trailing suspension element70, and tensioning element 106. FIG. 3 is an exploded perspectivedrawing of track-module apparatus 10.

FIG. 4 is a side-elevation drawing of track-module apparatus 10 with thenear (in the drawing) set of idler wheels 18 and 20 and bogie wheels 56,60 and 64 removed to show the various elements of embodiment 10 moreclearly.

FIG. 5 is side-elevation drawing of portions of vehicle track-moduleapparatus 10. Similar to FIG. 2, FIG. 5 illustrates various componentsof apparatus 10 with some components not shown to increase thevisibility of other components.

FIGS. 6A and 6B are perspective drawings of the bogie mount portions ofbogie assembly 46 of vehicle track-module apparatus 10 without bogiewheels 56, 60 and 64. FIG. 6A illustrates bogie mount 48 oriented as ifapparatus 10 were on a flat portion of the ground. FIG. 6B illustratesbogie mount 48 as if apparatus 10 were on uneven ground to illustratesome of the degrees-of-freedom available in the configuration of bogiemount 48 of bogie assembly 46. Further description is presented below inthis document.

The following description of track-module apparatus 10 (and later ofother embodiments) refers to FIGS. 1A-6B together. Note that in all ofthe drawings, a “+” symbol is used to indicate an axis of rotation. Ingeneral, as used herein, the term “axis” as stated above pertains to apivot joint which includes the necessary bearing structure and othercomponents to permit rotation about such axis. As an example, drivewheel axis 16 about which drive wheel 14 rotates is indicated in FIG. 4by a “+” symbol. Portions of axle and bearing structure (not shown)which are needed for drive wheel 14 to rotate around axis 16 are assumedto be part of embodiment 10.

In six instances within apparatus 10, the “+” symbol indicates a pivotjoint which may provide more than one degree-of-freedom of relativemotion. This is indicated by (a) the name including the word “pivot”rather than “axis” and (b) the relevant reference number ending with theletter “p”. These instances are 82 p, 84 p, 86 p, 88 p, 112 p and 116 p.As described later in this document, such higher number ofdegrees-of-freedom of relative motion may be provided by the use ofspherical bearings. It should be understood that it is intended that insome embodiments, such “pivots” may also simply be axes configured forsingle degree-of-freedom rotation. The use of the term “pivot” is notintended to limit the scope of the present invention to multipledegrees-of-freedom motion at such locations within embodiments havingsuch pivots. Acceptable components necessary to provide the requirednumber of degrees-of-freedom are well-known to those skilled in themechanical arts.

Leading suspension arm 24 is rotatably attached to frame 12 at a leadingarm axis 26 and extends forward to a leading-arm distal end 28 at whicha leading-wheel assembly 30 is rotatably attached. In apparatus 10,leading-wheel assembly 30 is also called leading-idler assembly 30 sincein apparatus 10, leading wheel 18 is leading idler wheel 18. Leadingsuspension arm 24 extends rearwardly to a rearward suspension end 32. Insimilar fashion, trailing suspension arm 34 is rotatably attached toframe 12 at a trailing arm axis 36 and extends rearward to atrailing-arm distal end 38 at which a trailing-wheel assembly 42 isattached. In apparatus 10, trailing-wheel assembly 42 is also calledtrailing-idler assembly 42 since in apparatus 10, trailing wheel 20 istrailing idler wheel 20.

In embodiment 10, trailing-idler assembly 42 primarily comprisestrailing idler wheels 20 which are rotatably attached at atrailing-idler axis 118. Trailing suspension arm 34 extends forwardly toa forward suspension end 40. In embodiment 10, leading arm axis andtrailing arm axis 36 are coincident and together form suspension-armaxis 44. Such coincidence is not intended to be limiting; otherconfigurations of the inventive track-module apparatus in which leadingarm axis 26 and trailing arm axis 36 are not coincident are contemplatedwithin the scope of this invention.

Suspension-arm axis 44 of embodiment 10 is shown as being rearward ofand below drive wheel axis 16 as defined by direction-of-travel arrow122 in FIG. 4. Such relative positioning with respect to drive wheelaxis 16 is not intended to be limiting; other relative positions ofleading arm axis 26 and trailing arm axis 36 are contemplated within thescope of this invention.

Bogie assembly 46 includes two leading bogie wheels 56, two middle bogiewheels 64, and two trailing bogie wheels 60. Bogie assembly 46 alsoincludes a bogie mount 48 which includes bogie-mount forward portion 50,a bogie-mount middle portion 54, a bogie-mount rearward portion 52, anda bogie-mount arm 102. Leading bogie wheels 56 are rotatable withrespect to bogie-mount forward portion 50 around a leading bogie axis58. In addition, leading bogie axis 58 rotates through a limited rangeof angles about a leading bogie roll axis 96 which is perpendicular toleading bogie axis 58.

In a similar fashion, such relative rotational movement is also providedfor middle bogie wheels 64 and trailing bogie wheels 60. Middle bogiewheels 64 are rotatable with respect to bogie-mount middle portion 54around a middle bogie axis 66. Middle bogie axis 66 rotates through alimited range of angles about a middle bogie roll axis 100 which isperpendicular to middle bogie axis 66. Trailing bogie wheels 60 arerotatable with respect to bogie-mount rearward portion 52 around atrailing bogie axis 62. Trailing bogie axis 62 rotates through a limitedrange of angles about a trailing bogie roll axis 98 which isperpendicular to trailing bogie axis 62.

Bogie mount 48 also includes bearings 96 b, 100 b and 98 b, configuredas follows: (1) bearing 96 b at leading bogie roll axis 96; (2) bearing100 b at middle bogie roll axis 100; and (3) bearing 98 b at trailingbogie roll axis 98. Bogie assembly 46 also includes a leading bogie axleassembly 96 a to which leading bogie wheels 56 are rotatably attached, amiddle bogie axle assembly 100 a to which middle bogie wheels 64 arerotatably attached, and a trailing bogie axle assembly 98 a to whichtrailing bogie wheels 60 are rotatably attached. Bearings 96 b, 100 band 98 b are configured to permit bogie axle assemblies 96 a, 100 a and98 a, respectively, to rotate on such bearings around leading bogie rollaxis 96, middle bogie roll axis 100 and trailing bogie roll axis 98,respectively. Leading bogie roll axis 96 and trailing bogie roll axis 98are indicated at respective ends of bogie mount 48 in FIGS. 6A and 6B.Also in FIGS. 6A and 6B, middle bogie roll axis 100 is indicated bydotted lines at middle bogie roll axis bearing 100 b but should beunderstood to be located internally in the center of bearing 100 b,parallel to such dotted lines and not on the surface of bearing 100 b.

Bogie mount 48 of bogie assembly 46 is rotatably attached at a firstbogie-assembly axis 78 to leading suspension arm 24 at a location alongarm 24 between leading arm axis 26 and leading-arm distal end 28 by abogie-assembly arm 72 at a bogie-assembly arm distal end 74.Bogie-assembly arm 72 also includes a bogie-assembly arm proximal end 76which is rotatably attached to a bogie-mount arm 102 of bogie mount 48at a second-bogie-assembly axis 80.

Bogie mount 48 of bogie assembly 46 is also attached to leadingsuspension arm 24 and trailing suspension arm 34 by suspension elements68 and 70. Leading suspension element 68 is rotatably attached torearward suspension end 32 of leading suspension arm 24 at a leadingsuspension-element pivot 82 p and is rotatably attached to bogie-mountrearward portion 52 at a first bogie-assembly pivot 84 p at a rearwardbogie-mount connection 92. Trailing suspension element 70 is rotatablyattached to forward suspension end 40 of trailing suspension arm 34 attrailing suspension-element pivot 86 p and is rotatably attached tobogie-mount forward portion 50 at a second bogie-assembly pivot 88 p ata forward bogie-mount connection 94.

Within bogie mount 48 of bogie assembly 46 in track-module apparatus 10,bogie-mount forward portion 50 and bogie-mount middle portion 54 arerotatably attached at a third bogie-assembly axis 90.

Embodiment 10 includes a tensioning element 106 which providesattachment between leading suspension arm 24 and leading-idler assembly30. Leading-idler assembly 30 includes leading idler wheels 18 and aleading-idler axis 104 about which leading idler wheels 18 rotate.Leading-idler assembly 30 also includes a wheel linkage 120 atleading-idler axis 104; in apparatus 10, wheel linkage 120 is idlerlinkage 120. Leading-arm distal end 28 is rotatably attached to idlerlinkage 120 at an idler offset axis 114 which is offset fromleading-idler axis 104.

A tensioning-element first end 108 of tensioning element 106 isrotatably attached to leading suspension arm 24 at a proximal tensioningpivot 112 p at forward suspension end 40 between leading-arm distal end28 and suspension-arm axis 44. A tensioning-element second end 110 isrotatably attached to leading-idler assembly 30 at a distal tensioningpivot 116 p offset from leading-idler axis 104. Idler offset axis 114 isparallel to leading-idler axis 104 and angularly displaced therearoundsuch that idler linkage 120 is a class 2 lever with idler offset axis114 being the fulcrum thereof. Tension forces on track 22 are providedthrough idler wheels 18 by tensioning element 106 through the class 2lever action of idler linkage 120 acted on by tensioning element 106.

Suspension elements 68 and 70 and tensioning element 106 may provideboth spring and damping forces. In some embodiments, such elements maybe gas-filled and include a liquid-filled cavity to provide both typesof forces for the suspension system. Such elements are well-known tothose skilled in the art of vehicle suspension. Further description ofsuspension elements 68 and 70 is provided in the description of FIG. 9.

FIGS. 7A through 8B illustrate the kinematics of track-module apparatus10 under various operating conditions. Each such drawing is aside-elevation illustration of apparatus 10 under representativeconditions to show the relative movement of the components of apparatus10 under such conditions. FIGS. 7A-7F illustrate the movement of vehicletrack-module apparatus 10 as it traverses over a small bump 126 on theground 124 along its path of travel. FIG. 7A shows track-moduleapparatus 10 just prior to encountering bump 126. FIG. 7B showsapparatus 10 with its leading idler wheels 18 over bump 126. FIG. 7Cshows apparatus 10 with leading bogie wheels 18 over bump 126. FIG. 7Dshows apparatus 10 with middle bogie wheels 64 over bump 126. FIG. 7Eshows apparatus 10 with trailing bogie wheels 60 over bump 126. FIG. 7Fshows apparatus 10 with trailing idler wheels 20 over bump 126.

FIG. 8A is a side-elevation drawing of track-module apparatus 10illustrating apparatus 10 as it traverses an uphill portion 128 ofground 124. Similarly, FIG. 8B is a side-elevation drawing of apparatus10 illustrating apparatus 10 as it traverses a downhill portion 130 ofground 124. Each of the drawings of FIGS. 7A through 8B illustrate idlerwheels 18 and 20 and bogie wheels 56, 60 and 64 all in contact withground 124 in order to support some portion of the loads on apparatus10.

FIG. 9 is a schematic drawing of leading suspension element 68 andtrailing suspension element 70 in a hydraulic circuit 134. Suspensionelements 68 and 70 each include cylinders hydraulic 136 containinghydraulic fluid 144 and gas-filled cylinders 138 containing gas 146separated by pistons 140. Hydraulic cylinders 136 and gas-filledcylinders 138 are movably sealed for relative movement by seals 142, andgas-filled cylinders 138 and pistons 140 are movably sealed for relativemovement by another set of seals 142 such that the volumes of hydraulicfluid 144 and gas 146 may both change under loads which are appliedacross suspension elements 68 and 70. In such components, gas 146 istypically nitrogen but other gases may be used.

Hydraulic cylinders 136 are interconnected by a hydraulic conduit 148placing suspension elements 68 and 70 in a common hydraulic circuit suchthat the pressures in suspension elements 68 and 70 are equal. Gas 146in gas-filled cylinders 138 enables suspension elements 68 and 70 toprovide spring forces to the suspension system of apparatus 10 whilehydraulic fluid 144 flowing through hydraulic conduit 148 enablessuspension elements 68 and 70 to provide damping forces to thesuspension system of apparatus 10.

Hydraulic circuit 134 also includes an external accumulator 150connected to hydraulic conduit 148 by an accumulator conduit 156.Accumulator 150 includes both hydraulic fluid 144 and gas 146 in sealedseparation from one another by an accumulator piston 152 movably sealedwithin accumulator 150 by accumulator seal 154. Gas 146 withinaccumulator 150 provides additional spring force to the suspensionsystem of apparatus 10 while hydraulic fluid 144 flowing throughaccumulator conduit 156 and hydraulic conduit 148 provides additionaldamping force to suspension system of apparatus 10.

Suspension elements 68 and 70 and tensioning element 106 may providesuspension forces which are variable. For example, the damping forcesmay depend on the direction of the movement (extension or contraction)of the element in order to provide a specific desired suspensionperformance.

The operation of the components of hydraulic circuit 134 are well-knownto those skilled in mechanical systems. FIG. 9 is intended only to beschematic. For example, the functions of accumulator piston 152 andaccumulator seal 154 may be provided by a membrane, a bladder or othersimilar component. In similar fashion, the components of suspensionelements 68 and 70 may also be different from those described abovewhile providing similar operation of suspension elements 68 and 70.

FIG. 10 is a schematic diagram of the embodiment of FIGS. 1A and 1B,illustrating a supported load FL and a set of five resulting wheel loadsF1 through F5. The load on leading wheels 18 is referred to as F1; theload on leading bogie wheels 56 is referred to as F2; the load on middlebogie wheels 64 is referred to as F3; the load on trailing bogie wheels60 is referred to as F4; and the load on trailing wheels 20 is referredto as F5. Since all of supported load FL acts on suspension-arm axis 44,FIG. 10 shows FL at such location in the schematic diagram of FIG. 10.

The load FL supported by track-module apparatus 10 may have bothvertical and horizontal components depending on the specific operationalsituation. These include at least the following: (a) the portion of thevehicle weight supported by apparatus 10; (b) pulling forces when thevehicle is pulling a load; and (c) braking forces which in an emergencybraking situation may be quite high. Also, of course, each of theresulting forces F1 through F5 may also have both vertical andhorizontal components, and all of these forces vary with the slope ofthe ground being traversed.

FIGS. 11 through 14 are side-elevation drawings (similar to FIG. 4)illustrating several alternative embodiments 10 a through 10 d,respectively, of the vehicle track-module apparatus of this invention.In each of FIGS. 11-14, the same reference numbers are used forcomponents similar to those of track-module apparatus 10.

FIG. 11 is a side-elevation drawing (similar to FIG. 4) of a firstalternative embodiment 10 a of the vehicle track-module apparatus ofthis invention. Embodiment 10 a is similar to embodiment 10 except thatmiddle bogie wheels 64 have been eliminated with corresponding changesin other components to accommodate such modification. A track modulesimilar to first alternative embodiment 10 a may be used to reducecomplexity and cost when compared to embodiment 10 and/or may be usedwhen the distance between the leading and trailing wheels needs to beshorter than is provided by embodiment 10.

FIG. 12 is a side-elevation drawing (similar to FIG. 4) of a secondalternative embodiment 10 b of the vehicle track-module apparatus ofthis invention. Embodiment 10 b is similar to first alternativeembodiment 10 a except that tensioning element 106 has been eliminatedand leading-idler assembly 30 primarily includes only leading idlerwheels 18. A track module similar to second alternative embodiment 10 bmay be used to reduce complexity and cost when compared to embodiment10. Similar to first embodiment 10 a, second embodiment 10 b may alsoprovide a shorter distance between the leading and trailing wheels ifsuch a configuration is desirable.

FIG. 13 is a side-elevation drawing (similar to FIG. 4) of a thirdalternative embodiment 10 c of the vehicle track-module apparatus ofthis invention. Embodiment 10 c is similar to embodiment 10 except thattensioning element 106 has been eliminated and leading-idler assembly 30primarily includes only leading idler wheels 18. A track module similarto third alternative embodiment 10 c may be used to reduce complexityand cost when compared to embodiment 10.

FIG. 14 is a side-elevation drawing (similar to FIG. 4) of a fourthalternative embodiment 10 d of the vehicle track-module apparatus ofthis invention. Embodiment 10 d is similar to third alternativeembodiment 10 c except that third bogie-assembly axis 90 has beeneliminated with corresponding changes in other components to accommodatesuch modification. A track module similar to fourth alternativeembodiment 10 d may be used to reduce complexity and cost when comparedto embodiment 10. In the case of fourth embodiment 10 d, adegree-of-freedom within bogie assembly 46 has been removed; undercertain operational conditions such as travel mainly on generally eventerrain, this reduction in compliance may be acceptable.

FIG. 15A is side-elevation drawing of portions of vehicle track-moduleapparatus 10 to illustrate the detail of tensioning-element first end108 of tensioning element 106. FIG. 15B is a sectional view (sectionA-A) as indicated in FIG. 15A. Section A-A passes through proximaltensioning pivot 112 p at the rotatable attachment between tensioningelement 106 and leading suspension arm 24.

FIG. 15C is a further enlargement of a portion of FIG. 15B to show evenmore detail of proximal tensioning pivot 112 p. As described above,certain pivot joints within apparatus 10 involve structures whichprovide more than one degree-of-freedom of rotation. In the namingconvention used herein, the word “pivot” is used for such more than onedegree-of-freedom connections. Within apparatus 10, these include 82 p,84 p, 86 p, 88 p, 112 p and 116 p, and FIGS. 15A-15C are used toillustrate one such pivot. In embodiment 10, all such pivots arespherical bearings as is shown for pivot 112 p.

Referring to FIG. 15C, proximal tensioning pivot 112 p includes aspherical bearing which includes a ball 112 b which rotates in a socket112 s on leading suspension arm 24. A mechanical connector 112 c holdsball 112 c in socket 112 s.

By using the inventive structure of the various embodiments oftrack-module apparatus disclosed herein and by selecting the dimensionsof the various components, a track-module designer is able to set theload distribution on the ground-engaging wheels to meet the requirementsof a particular vehicle application. For example, it may be desirable tohave the leading or trailing wheels take somewhat different percentagesof the load on the vehicle. And often it is desirable, when theapparatus has more than one bogie-wheel axle, to have each of thebogie-wheel axles support substantially the same vehicle load. A set oflinkage dimensions can be chosen to distribute the load supported by thebogies as desired.

Kinematic analysis methods well-known to those skilled in the art ofmechanical systems can be used to evaluate the load-distributionperformance of a specific set of linkage dimensions in apparatus 10. Inthe example described below and in FIGS. 17A and 17B, such analysis wasused to compute the load distribution under a set of different loadconditions. Referring to the schematic diagram of FIG. 10, thedimensions are represented by the following notation. A horizontaldimension includes the letter “H” followed by two reference numbersseparated by a colon. Thus, H44:118 is the horizontal distance fromsuspension axis 44 to trailing-idler axis 118. The letter “V” indicatesa vertical dimension, and the letter “D” a diameter. FIG. 17A summarizesa set of dimensions for a representative configuration of track-moduleapparatus 10 with suspension elements 68 and 70 in common hydrauliccircuit 134.

FIG. 17B summarizes the results of analysis of the representativeexample of FIG. 17A. As can be seen, in this example, the loads F2, F3and F4 on bogie wheels 56, 64 and 60, respectively, are and remainevenly distributed among the bogie wheels, and the addition of variousportions of the total loading from vehicle weight, track tension,braking and pull cause very modest changes to the load distributionpercentages.

The power source for the track-module apparatus of this invention is notlimited to a rotating power shaft of the vehicle. Other power-sourceconfigurations are contemplated by this invention, such as a hydraulicmotor or other power source on the vehicle or a mechanical, hydraulic orother power source directly mounted on the apparatus itself

FIG. 18 is a schematic diagram showing an embodiment 10 t of theinventive track-module apparatus in which tensioning element 106 ismounted with respect to trailing idler wheel 20, and trailing-idlerassembly 42 includes additional linkage elements. Also, leading-wheelassembly 30 is simplified accordingly.

In embodiment 10 t, tensioning element 106 provides attachment betweentrailing suspension arm 34 and trailing-idler assembly 42.Trailing-idler assembly 42 includes trailing idler wheels 20 andtrailing-idler axis 118 about which trailing idler wheels 20 rotate.Trailing-idler assembly 42 includes wheel linkage 120 at trailing-idleraxis 118; in apparatus 10 t, wheel linkage 120 is idler linkage 120.Trailing-arm distal end 38 is rotatably attached to idler linkage 120 atan idler offset axis 114 which is offset from trailing-idler axis 118.

Tensioning-element first end 108 of tensioning element 106 is rotatablyattached to trailing suspension arm 34 at proximal tensioning pivot 112p at rearward suspension end 32 between trailing-arm distal end 38 andsuspension-arm axis 44. Tensioning-element second end 110 is rotatablyattached to trailing-idler assembly 42 at distal tensioning pivot 116 poffset from leading-idler axis 118. Idler offset axis 114 is parallel toleading-idler axis 118 and angularly displaced therearound such thatidler linkage 120 is a class 2 lever with idler offset axis 114 beingthe fulcrum thereof. Tension forces on track 22 are provided throughidler wheels 20 by tensioning element 106 through the class 2 leveraction of idler linkage 120 acted on by tensioning element 106.

It may be desirable to have a tensioning element related to each of theleading and trailing wheel assemblies when certain performancerequirements need to be addressed.

While the principles of this invention are shown and described here inconnection with specific embodiments, it is to be understood that suchembodiments are by way of example and are not limiting.

The invention claimed is:
 1. In vehicle track-module apparatus includinga module frame, a drive wheel rotatable with respect to the frame,leading and trailing ground-engaging wheels and at least oneground-engaging bogie wheel therebetween, and an endless track extendingaround the wheels and driven by the drive wheel, the improvementcomprising: a leading suspension arm rotatably attached to the frame ata leading arm axis and extending forwardly to a leading-arm distal endat which a leading-wheel assembly is rotatably attached and rearwardlyto a rearward suspension end; a trailing suspension arm rotatablyattached to the frame at a trailing arm axis and extending rearwardly toa trailing-arm distal end at which a trailing-wheel assembly isrotatably attached and forwardly to a forward suspension end; a bogieassembly having a bogie mount and the at least one bogie wheel rotatablewith respect thereto; and leading and trailing suspension elementsrotatably attached to and extending from the rearward and forwardsuspension ends, respectively, to rearward and forward rotatablebogie-mount connections, respectively.
 2. The vehicle track-moduleapparatus of claim 1 wherein the leading-arm and trailing-arm axescoincide at a suspension-arm axis.
 3. The vehicle track-module apparatusof claim 2 wherein the drive wheel is rotatable about a drive wheel axisand the suspension-arm axis is at a level lower than the drive wheelaxis.
 4. The vehicle track-module apparatus of claim 3 wherein thesuspension-arm axis is rearward of the drive wheel axis.
 5. The vehicletrack-module apparatus of claim 1 wherein: the bogie assembly furtherincludes a bogie-assembly arm rotatably attached (a) at a bogie-assemblyarm distal end to the leading suspension arm at a first bogie-assemblyaxis between the leading-arm distal end and the suspension-arm axis and(b) at a bogie-assembly arm proximal end to the bogie mount at a secondbogie-assembly axis; the leading suspension element is rotatablyattached (a) to the rearward suspension end at a leadingsuspension-element pivot and (b) to the rearward bogie-mount connectionat a first bogie-assembly pivot; and the trailing suspension element isrotatably attached (a) to the forward suspension end at a trailingsuspension-element pivot and (b) to the forward bogie-mount connectionat a second bogie-assembly pivot.
 6. The vehicle track-module apparatusof claim 5 wherein the at least one bogie wheel includes at least oneleading bogie wheel and at least one trailing bogie wheel, and the bogiemount includes: a bogie-mount forward portion having the at least oneleading bogie wheel attached thereto at a leading bogie axis, thebogie-mount forward portion including the forward bogie-mountconnection; and a bogie-mount rearward portion having the at least onetrailing bogie wheel attached thereto at a trailing-bogie axis, thebogie-mount rearward portion including the rearward bogie-mountconnection.
 7. The vehicle track-module apparatus of claim 6 includingat least two leading bogie wheels and at least two trailing bogie wheelsand wherein the leading bogie axis rotates on a leading bogie roll axisperpendicular thereto and the trailing bogie axis rotates on a trailingbogie roll axis perpendicular thereto.
 8. The vehicle track-moduleapparatus of claim 6 wherein the bogie-mount forward and rearwardportions are rotatably attached at a third bogie-assembly axis.
 9. Thevehicle track-module apparatus of claim 6 wherein the bogie mountfurther includes a bogie-mount middle portion having at least one middlebogie wheel attached thereto at a middle bogie axis.
 10. The vehicletrack-module apparatus of claim 9 including at least two leading bogiewheels, at least two trailing bogie wheels, and at least two middlebogie wheels and wherein: the leading bogie axis rotates on a leadingbogie roll axis perpendicular thereto; the middle bogie axis rotates ona middle bogie roll axis perpendicular thereto; and the trailing bogieaxis rotates on a trailing bogie roll axis perpendicular thereto. 11.The vehicle track-module apparatus of claim 10 wherein the bogie-mountforward and middle portions are rotatably attached at a thirdbogie-assembly axis.
 12. The vehicle track-module apparatus of claim 1further including a tensioning element having first and second ends, thefirst end rotatably attached to the leading suspension arm at a proximaltensioning pivot between the leading-arm distal end and the leading armaxis, and wherein the leading-wheel assembly includes: at least oneleading wheel rotatable about a leading-wheel axis; and a wheel linkageat the leading-wheel axis, the distal end of the leading suspension armbeing rotatably attached to the wheel linkage at a wheel offset axisoffset from the leading-wheel axis, the second end of the tensioningelement being rotatably attached to the wheel linkage at a distaltensioning pivot which is offset from the leading-wheel axis, the distaltensioning pivot and the wheel offset axis being angularly displacedaround the leading-wheel axis such that the wheel linkage is a class 2lever with the wheel offset axis being the fulcrum thereof.
 13. Thevehicle track-module apparatus of claim 12 wherein the trailing-wheelassembly includes a trailing-wheel axis at the trailing-arm distal endand at least one trailing wheel rotatable about the trailing-wheel axis.14. The vehicle track-module apparatus of claim 12 wherein the proximaland distal tensioning pivots are configured to permit rotation having atleast two degrees-of-freedom.
 15. The vehicle track-module apparatus ofclaim 1 wherein: rotatable attachments of the leading and trailingsuspension elements at the rearward and forward suspension ends,respectively, are configured to permit rotation having at least twodegrees-of-freedom; and the rearward and forward rotatable bogie-mountconnections are configured to permit rotation having at least twodegrees-of-freedom.
 16. The vehicle track-module apparatus of claim 1further including rotatable attachments of the leading and trailingsuspension elements to the frame at the rearward and forward suspensionends, respectively, which are configured to permit rotation having atleast two degrees-of-freedom and the rearward and forward rotatablebogie mount connections are configured to permit rotation having atleast two degrees-of-freedom.
 17. The vehicle track-module apparatus ofclaim 1 wherein the leading and trailing suspension elements eachinclude gas-filled components to provide spring force.
 18. The vehicletrack-module apparatus of claim 17 wherein the leading and trailingsuspension elements each further include hydraulic components.
 19. Thevehicle track-module apparatus of claim 18 wherein the leading andtrailing suspension elements are on a common hydraulic circuit.
 20. Thevehicle track-module apparatus of claim 19 further including an externalaccumulator hydraulically connected to the common hydraulic circuit. 21.The vehicle track-module apparatus of claim 1 wherein the leading andtrailing wheels have diameters which are substantially the same as eachother.
 22. The vehicle track-module apparatus of claim 1 includingplural bogie wheels and wherein the bogie wheels have diameters whichare substantially the same as each other.
 23. The vehicle track-moduleapparatus of claim 1 further including a tensioning element having firstand second ends, the first end rotatably attached to the trailingsuspension arm at a proximal tensioning pivot between the trailing-armdistal end and the trailing arm axis, and wherein the trailing-wheelassembly includes: at least one trailing wheel rotatable about atrailing-wheel axis; and a wheel linkage at the trailing-wheel axis, thedistal end of the trailing suspension arm being rotatably attached tothe wheel linkage at a wheel offset axis offset from the trailing-wheelaxis, the second end of the tensioning element being rotatably attachedto the wheel linkage at a distal tensioning pivot which is offset fromthe trailing-wheel axis, the distal tensioning pivot and the wheeloffset axis being angularly displaced around the trailing-wheel axissuch that the wheel linkage is a class 2 lever with the wheel offsetaxis being the fulcrum thereof.
 24. The vehicle track-module apparatusof claim 23 wherein the leading-wheel assembly includes a leading-wheelaxis at the leading-arm distal end and at least one leading wheelrotatable about the leading-wheel axis.
 25. The vehicle track-moduleapparatus of claim 23 wherein the proximal and distal tensioning pivotsare configured to permit rotation having at least twodegrees-of-freedom.
 26. In vehicle track-module apparatus including amodule frame, leading and trailing ground-engaging idler wheels and atleast one ground-engaging bogie wheel therebetween, a drive wheelpositioned above and between the idler wheels and rotatable with respectto the frame, and an endless track extending around the wheels anddriven by the drive wheel, the improvement comprising: a leadingsuspension arm rotatably attached to the frame at a leading arm axis andextending forwardly to a leading-arm distal end at which a leading-idlerassembly is rotatably attached and rearwardly to a rearward suspensionend; a trailing suspension arm rotatably attached to the frame at atrailing arm axis and extending rearwardly to a trailing-arm distal endat which a trailing-idler assembly is rotatably attached and forwardlyto a forward suspension end; a bogie assembly having a bogie mount andthe at least one bogie wheel rotatable with respect thereto; and leadingand trailing suspension elements rotatably attached to and extendingfrom the rearward and forward suspension ends, respectively, to rearwardand forward rotatable bogie-mount connections, respectively.
 27. Thevehicle track-module apparatus of claim 26 wherein the leading-arm andtrailing-arm axes coincide at a suspension-arm axis.
 28. The vehicletrack-module apparatus of claim 27 wherein the drive wheel is rotatableabout a drive wheel axis and the suspension-arm axis is at a level lowerthan the drive wheel axis.
 29. The vehicle track-module apparatus ofclaim 28 wherein the suspension-arm axis is rearward of the drive wheelaxis.
 30. The vehicle track-module apparatus of claim 26 wherein: thebogie assembly further includes a bogie-assembly arm rotatably attached(a) at a bogie-assembly arm distal end to the leading suspension arm ata first bogie-assembly axis between the leading-arm distal end and thesuspension-arm axis and (b) at a bogie-assembly arm proximal end to thebogie mount at a second bogie-assembly axis; the leading suspensionelement is rotatably attached (a) to the rearward suspension end at aleading suspension-element pivot and (b) to the rearward bogie-mountconnection at a first bogie-assembly pivot; and the trailing suspensionelement is rotatably attached (a) to the forward suspension end at atrailing suspension-element pivot and (b) to the forward bogie-mountconnection at a second bogie-assembly pivot.
 31. The vehicletrack-module apparatus of claim 30 wherein the at least one bogie wheelincludes at least one leading bogie wheel and at least one trailingbogie wheel, and the bogie mount includes: a bogie-mount forward portionhaving the at least one leading bogie wheel attached thereto at aleading bogie axis, the bogie-mount forward portion including theforward bogie-mount connection; and a bogie-mount rearward portionhaving the at least one trailing bogie wheel attached thereto at atrailing-bogie axis, the bogie-mount rearward portion including therearward bogie-mount connection.
 32. The vehicle track-module apparatusof claim 31 including at least two leading bogie wheels and at least twotrailing bogie wheels and wherein the leading bogie axis rotates on aleading bogie roll axis perpendicular thereto and the trailing bogieaxis rotates on a trailing bogie roll axis perpendicular thereto. 33.The vehicle track-module apparatus of claim 31 wherein the bogie-mountforward and rearward portions are rotatably attached at a thirdbogie-assembly axis.
 34. The vehicle track-module apparatus of claim 31wherein the bogie mount further includes a bogie-mount middle portionhaving at least one middle bogie wheel attached thereto at a middlebogie axis.
 35. The vehicle track-module apparatus of claim 34 includingat least two leading bogie wheels, at least two trailing bogie wheels,and at least two middle bogie wheels and wherein: the leading bogie axisrotates on a leading bogie roll axis perpendicular thereto; the middlebogie axis rotates on a middle bogie roll axis perpendicular thereto;and the trailing bogie axis rotates on a trailing bogie roll axisperpendicular thereto.
 36. The vehicle track-module apparatus of claim35 wherein the bogie-mount forward and middle portions are rotatablyattached at a third bogie-assembly axis.
 37. The vehicle track-moduleapparatus of claim 26 further including a tensioning element havingfirst and second ends, the first end rotatably attached to the leadingsuspension arm at a proximal tensioning pivot between the leading-armdistal end and the leading arm axis, and wherein the leading-wheelassembly includes: at least one leading idler wheel rotatable about aleading-idler axis; and an idler linkage at the leading-idler axis, thedistal end of the leading suspension arm being rotatably attached to theidler linkage at an idler offset axis offset from the leading-idleraxis, the second end of the tensioning element being rotatably attachedto the idler linkage at a distal tensioning pivot which is offset fromthe leading-idler axis, the distal tensioning pivot and the idler offsetaxis being angularly displaced around the leading-idler axis such thatthe idler linkage is a class 2 lever with the idler offset axis beingthe fulcrum thereof.
 38. The vehicle track-module apparatus of claim 37wherein the trailing-idler assembly includes a trailing-idler axis atthe trailing-arm distal end and at least one trailing idler wheelrotatable about the trailing-idler axis.
 39. The vehicle track-moduleapparatus of claim 37 wherein the proximal and distal tensioning pivotsare configured to permit rotation having at least twodegrees-of-freedom.
 40. The vehicle track-module apparatus of claim 26wherein: rotatable attachments of the leading and trailing suspensionelements at the rearward and forward suspension ends, respectively, areconfigured to permit rotation having at least two degrees-of-freedom;and the rearward and forward rotatable bogie-mount connections areconfigured to permit rotation having at least two degrees-of-freedom.41. The vehicle track-module apparatus of claim 26 further includingrotatable attachments of the leading and trailing suspension elements tothe frame at the rearward and forward suspension ends, respectively,which are configured to permit rotation having at least twodegrees-of-freedom and the rearward and forward rotatable bogie-mountconnections are configured to permit rotation having at least twodegrees-of-freedom.
 42. The vehicle track-module apparatus of claim 26wherein the leading and trailing idler wheels have diameters which aresubstantially the same.
 43. The vehicle track-module apparatus of claim26 including plural bogie wheels and wherein the bogie wheels havediameters which are substantially the same.
 44. The vehicle track-moduleapparatus of claim 26 configured such that the drive wheel is driven bya driving mechanism powered by a vehicle.
 45. The vehicle track-moduleapparatus of claim 44 wherein the driving mechanism is a gearboxattachable to a driven axle of the vehicle.
 46. The vehicle track-moduleapparatus of claim 26 further including a tensioning element havingfirst and second ends, the first end rotatably attached to the trailingsuspension arm at a proximal tensioning pivot between the trailing-armdistal end and the trailing arm axis, and wherein the trailing-wheelassembly includes: at least one trailing idler wheel rotatable about atrailing-idler axis; and an idler linkage at the trailing-idler axis,the distal end of the trailing suspension arm being rotatably attachedto the idler linkage at an idler offset axis offset from thetrailing-idler axis, the second end of the tensioning element beingrotatably attached to the idler linkage at a distal tensioning pivotwhich is offset from the trailing-idler axis, the distal tensioningpivot and the idler offset axis being angularly displaced around thetrailing-idler axis such that the idler linkage is a class 2 lever withthe idler offset axis being the fulcrum thereof.
 47. The vehicletrack-module apparatus of claim 46 wherein the leading-idler assemblyincludes a leading-idler axis at the leading-arm distal end and at leastone leading idler wheel rotatable about the leading-idler axis.
 48. Thevehicle track-module apparatus of claim 46 wherein the proximal anddistal tensioning pivots are configured to permit rotation having atleast two degrees-of-freedom.